Capsule technique offers more efficient option for power plant CCS

Researchers have developed a class of materials that enable a safer, cheaper, and more energy-efficient process for removing greenhouse gas from power plant emissions. 

It is claimed the approach could be an important advance in carbon capture and sequestration (CCS).

The team, led by scientists from Harvard University, Massachusetts and Lawrence Livermore National Laboratory (LLNL), California, employed a microfluidic assembly technique to produce microcapsules that contain liquid sorbents encased in highly permeable polymer shells. They have significant performance advantages over the carbon-absorbing materials used in current CCS technology.

The work is described in a paper published online today in the journal Nature Communications.

‘Microcapsules have been used in a variety of applications – for example, in pharmaceuticals, food flavouring, cosmetics, and agriculture – for controlled delivery and release, but this is one of the first demonstrations of this approach for controlled capture,’ said Jennifer A. Lewis, the Hansjörg Wyss Professor of Biologically Inspired Engineering at the Harvard School of Engineering and Applied Sciences (SEAS) and a co-lead author.

Current carbon capture technology uses caustic amine-based solvents to separate CO2 from the flue gas escaping a facility’s smokestacks. But state-of-the-art processes are expensive, result in a significant reduction in a power plant’s output, and yield toxic by-products.

The new technique employs sodium carbonate, an abundant and environmentally benign sorbent. The microencapsulated carbon sorbents (MECS) are said to achieve an order-of-magnitude increase in CO2 absorption rates compared to sorbents currently used in carbon capture. According to a statement, another advantage is that amines break down over time, while carbonates have a virtually limitless shelf life.

‘MECS provide a new way to capture carbon with fewer environmental issues,’ said Roger D. Aines, leader of the fuel cycle innovations program at LLNL and a co-lead author. ‘Capturing the world’s carbon emissions is a huge job; we need technology that can be applied to many kinds of carbon dioxide sources with the public’s full confidence in the safety and sustainability.’

Researchers at LLNL and the US Department of Energy’s National Energy Technology Lab are now working on enhancements to the capture process to bring the technology to scale.

The emission-scrubbing potential of CCS is not limited to the electric generation sector; Aines said that the MECS-based approach can also be tailored to industrial processes like steel and cement production.

MECS are produced using a double capillary device in which the flow rates of three fluids – a carbonate solution combined with a catalyst for enhanced CO2 absorption, a photocurable silicone that forms the capsule shell, and an aqueous solution – can be independently controlled.

‘Encapsulation allows you to combine the advantages of solid capture media and liquid capture media in the same platform,’ said Lewis. ‘It is also quite flexible, in that both the core and shell chemistries can be independently modified and optimized.’

Funding for the encapsulated liquid carbonates work was provided by the Innovative Materials and Processes for Advanced Carbon Capture Technology program of the US Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E).